Pressure–temperature limit for APR-1400 reactor pressure vessel nozzles

Abstract

The reactor pressure vessel (RPV) is a critical component of nuclear power plants (NPPs), designed to endure high temperatures and pressures to prevent coolant leakage. During operation, the RPV is irradiated by fast neutrons (E > 1 MeV), which reduces the fracture toughness of its materials. Regulatory rules require monitoring the neutron irradiation embrittlement to ensure the fracture toughness satisfies the criteria throughout the plant design life and these rules also require evaluating the pressure–temperature (P–T) limit curves considering the neutron irradiation embrittlement. Traditionally, P–T limit curves have been developed based on the beltline region, which is mostly affected by the neutron exposure. However, the geometric discontinuities of the RPV nozzles cause the higher stresses in that region, which potentially requires more conservative operating limits. In this study, P–T limit curves for APR-1400 (Advanced Power Reactor 1400) RPV nozzles are developed using the finite element analysis (FEA) model and the resultant stress intensity factor under internal pressure and cooldown conditions. These nozzle P–T limit curves are also compared to the traditional beltline region P–T limit curves.